Affinity of Cytotoxic Copper(II) Complex to Bovine Serum Albumin

The interaction of water soluble copper(II) complex, [Cu(dipica)(CH3COO)]ClO4 (1), where dipica is di-(2-picolyl)amine, as in vitro cytotoxic agent, with bovine serum albumin (BSA) has been studied by fluorescence, UV-Vis absorption and circular dichroism (CD) spectroscopic techniques at pH 7.4. The quenching constants and binding parameters such as binding constants and number of binding sites were determined by fluorescence quenching method. The obtained results proved that the fluorescence quenching of BSA by 1 was a result of the formation of a non-fluorescent BSA-1 system with the binding constants of 1.81 x 10-5 M-1 and 2.10 x 10-5 M-1 at 300 K and 310 K respectively. The calculated thermodynamic parameters (G°, H° and S°) confirmed that the binding reaction is mainly entropy-driven and hydrophobic forces played major role in the reaction. The distance, r, between the donor (BSA) and acceptor (1) was obtained according to the Forster theory of nonradiative energy transfer. On the other hand, structural analysis indicates that binding of 1 resulting in a higher change in the local polarity around tryptophan rather than tyrosine residues of BSA as revealed by synchronous fluorescence spectra and a decrease in ï�¡-helix as revealed by the far-UV CD spectra.